| In this paper,a soft rock tunnel with high ground stress was used as the research background and its deformation pattern was analysed and summarised in conjunction with the field monitoring datas.Theoretical calculations were used to estimate the relevant parameters of the yield pressure support system.Based on the calculation results,the design of the yield pressure device was optimized and the yield pressure support system was established to compare with the traditional rigid support system,so that the support characteristics of the yield pressure support system could be discussed.Finally,a sensitivity analysis was conducted on the relevant parameters of the yield pressure support system.The results of the study can be used as a design reference for the establishment of the yield pressure support system.The above researches mainly draw the following conclusions:(1)Engineering deformation pattern: from the monitoring results of each monitoring point,the deformation values in the horizontal direction are greater than those in the vertical direction.The tunnel is in an unfavourable state of complete partial pressure,and the surrounding rocks on the right side are more severely loosened than those on the left side.The degree of loosening of the surrounding rocks on the left and right sides is greater than that of the surrounding rocks on the upper and lower sides of the tunnel,and the shape of the loosening circle profile is irregular.(2)Parameters of support system: by enhancing the rigidity of the initial support,the support system has a good deformation control effect,but the spacing between the steel arch used is small.The whole process of resistance-deformation-resistance of the yield pressure support system allows for further release of the rock pressure and finally reaches a state of equilibrium.The deformation of the tunnel was estimated by taking into account the stress characteristics of the surrounding rock,the ground stress and the resistance of the support system,and the value of deformation in the ring was251.33 mm,meanwhile,the working resistance of the yield pressure device was not greater than 453.12 k N.(3)Optimization of yield pressure device: compared to the original square tube pre-folded yield pressure device,the peak load of the new combined yield pressure device is basically unchanged,the material utilisation rate is increased by 4.18%,and the fluctuation of the reaction force during the energy-absorbing let-down process is reduced by 19.69%.The energy evolution principle of the symmetrical metal thin-walled tube calculates the reaction force with high accuracy.The error in the critical position of the calculation is no more than 6.25%,the relative error in the reaction force is no more than 7.91%,the relative error in the total energy is 7.06%and the yield pressure characteristics of the double-layer symmetrical thin-walled metal tube are relatively optimal.(4)Effect of yield pressure support: compared with the traditional rigid support,the application of the yield pressure device can effectively make the plastic zone of the surrounding rock,the stress of the steel arch and the internal force of the initial support more uniformly distributed,and the plastic damage area of the steel arch is reduced by more than 40.57%;however,in terms of deformation control effect,the deformation volume at each position increases,but the increase is within 20.08%;the energy absorption ratio of the steel arch increases by more than 27.39%.With the increase in the spacing of the steel arch,the volume of the plastic zone is increasing and the profile is more regular,the displacement of the surrounding rock in all directions has increased but the increase is not more than 1.11%,the internal force of the steel arch and the distribution of stress in the steel arch are becoming more and more discrete,and the yielding ratio of the steel arch is generally on the rise.Combining all aspects of support effectiveness,the steel arch spacing of 0.6 m was adopted for the design analysis.(5)Optimization of support system: the application of the yield pressure device can reduce the thickness of the plastic zone of the surrounding rock at the location,so the yield pressure device should be arranged at the location where the thickness of the plastic zone is larger.If the working resistance of the yield pressure device and the travel of the yield pressure device are certain,changes in the position of the yield pressure device alone will have little effect on the displacement of the surrounding rock in all directions.The yield pressure device reduces the axial force of the initial support at the applied position,increases the inner stress and reduces the outer stress at the steel arch position.For this project,it is better to place the yield pressure device at the top and bottom of the steel arch,the left and right side walls than at the left and right arch foot and left and right arch waist. |
